WASHINGTON — AT&T, the largest U.S. telephone company, may need to offer more concessions to clear the last regulatory hurdle in its $85 billion purchase of BellSouth.

A Federal Communications Commission member, Robert McDowell, a Republican, said Monday that he would not vote to break an impasse on the merger, because his past work as a lobbyist would raise ethical questions. The other two Republicans and two Democrats on the panel must now restart the talks.

The Democratic members, Michael Copps and Jonathan Adelstein, are demanding conditions from AT&T like price controls and airwave-license sales, moves that are being resisted by the chairman, Kevin Martin, and the other Republican commissioner, Deborah Taylor Tate. AT&T and BellSouth had anticipated approval by year-end.

"The Democratic hand in the merger negotiations has been strengthened significantly," said Paul Glenchur, an analyst at Stanford Washington Research Group in Washington. "It won't mean the deal will fail. There will have to be more aggressive concessions to get the deal done quickly."

AT&T has offered concessions including a 30-month price freeze on certain business services, $10-a-month high-speed Internet access for some BellSouth customers and expanded broadband access in rural and low-income areas.

"We have sought the support for this merger from every member of the Commission since the very beginning, and we will continue to do so," an AT&T spokesman Michael Balmoris, said. "We will — as we have always done — do our part to bring the merger review to a bipartisan completion as quickly as possible."

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Martin on Dec. 1 asked Samuel Feder, the general counsel of the commission, to decide whether it would be in the government's interest for McDowell to cast a tie-breaking vote. Feder ruled Dec. 8 that it would be. Feder called the decision "difficult" and said his opinion did not compel McDowell to vote.

"My four colleagues have exclusive and unambiguous ownership of this important merger," McDowell said at a news conference Monday. "I urge all of them to resolve their differences as soon as possible."

The trade group Comptel, McDowell's former employer, has urged regulators to reject the BellSouth deal or set tougher conditions than AT&T has offered, like price controls for at least seven years and a "net neutrality" requirement that would bar AT&T from charging Web companies premium fees for faster services. The Washington-based Comptel represents companies that compete with AT&T, based in San Antonio, Texas, and the Atlanta-based BellSouth.

The BellSouth deal would expand AT&T's local service area to 22 states. The purchase would also give AT&T full ownership of Cingular Wireless, the largest U.S. mobile phone carrier.